This has been on my mind for quite a while now... Is it really crucial to be able to crunch numbers on the fly?
I have considerate difficulty making out the quotient of $1 / 0.732 $ for example. I can approximate it well, but still (~1.3...). When I go for precision, I am too slow.
Are there techniques to accelerate arithmetic operations?
Doerfler's book Dead Reckoning: Calculating Without Instruments contains algorithms specifically designed for computing nontrivial things mentally. But it's still not easy and requires quite a lot of practice, I guess. To begin with, one must be really good at multiplying two-digit numbers (so I'm lost there already...).